Footed container and base therefor

ABSTRACT

A molded polymeric container that is shaped to exhibit superior characteristics of light weighting, stability against toppling and resistance to stress cracking includes a conventional cylindrical body portion having a longitudinal axis and a circumferential sidewall and a novel bottom portion. The bottom portion includes a central pushup area of uniformity that is substantially uniform within a spatial rotation about the longitudinal axis. The area of uniformity has a radius R G . The bottom also includes a plurality of support feet that surround and protrude downwardly from the pushup area. Each of the support feet have a bottom support surface with an inner point of contact and an outer point of contact. The outer points of contact together define an outer contact radius R OC . The bottom portion as a whole has a radius of maximum width R BASE . A plurality of ribs are positioned in valleys between the support feet. Each of these ribs is positioned between and helps define two of the support feet. At least one of the ribs has a localized radius of curvature R c  that intersects an arc connecting inner points of contact of two adjacent support feet. Advantageously, the radius of uniformity is within the range of about 16% to about 26% of R OC ; and R C  is within the range of about 70% to about 1 10% of R BASE .

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates broadly to the field of container making,and more specifically to blow molded plastic bottles, such as the PETbottles that are in common use today for packaging soft drinks such assoda. More specifically, the invention relates to an improved footedcontainer and bottom therefor that exhibits superior characteristics oflight weighting, stability and resistance to stress cracking.

[0003] 2. Description of the Related Technology

[0004] During the last twenty-five years or so, there has been adramatic shift in the packaging of carbonated beverages, particularly,soft drinks, away from glass containers and toward plastic containers.The plastic containers initially took the form of a two-piececonstruction, wherein a plastic bottle having a generally hemisphericalbottom was applied a separate base cup, which would permit the bottle tobe stood upright. The hemispherical bottom was seen as the mostdesirable shape for retaining the pressure generated by the carbonationwithin the container. Pressures in such containers can rise to 100p.s.i. or more when the bottled beverage is exposed to the sun, storedin a warm room, car trunk, or the like.

[0005] Such plastic containers represented a significant safetyadvantage over glass containers when exposed to the same internalpressures. However, the two-piece construction was not economicalbecause it required a post molding assembly step, and, also a separationstep prior to reclaiming or recycling the resins forming the bottle andbase cup.

[0006] During this period of development, various attempts were made toconstruct a one-piece, self-supporting container that would be able toretain the carbonated beverages at the pressures involved. Such aone-piece container requires the design of a base structure which willsupport the bottle in an upright position and will not bulge outwardlyat the bottom. A variety of designs were first attempted, with mostfollowing one of two principal lines of thought. One line of designsinvolved a so-called champagne base having a complete annular peripheralring. Examples of such bottles are found in U.S. Pat. Nos. 3,722,726;3,881,621; 4,108,324; 4,247,012; and, 4,249,666. Another variety ofdesigns is that which included a plurality of feet protruding downwardfrom a curved bottom. Examples of this variety are to be found in U.S.Pat. Nos. 3,598,270; 4,294,366; 4,368,825; 4,865,206; and, 4,867,323. Inrecent years, the latter type of design has achieved primacy in themarketplace.

[0007] Footed one piece bottles present certain problems, though, thathave not yet been worked out to the satisfaction of the packagingindustry and its customers. For example, the uneven orientation of thepolymer in the footed area of the bottom can contribute to unevenpost-filling expansion of either one or more feet or the central portionof the bottom, creating what is generally referred to as a “rocker.” Inaddition, the presence of the feet themselves and the need to force theoriented material into the shape of the feet can create stress points inthe container bottom that can adversely affect container shape.Container bottom designs that minimize stress and disorientation of thepolymer during molding, then are considered preferable.

[0008] Another concern in the design of container bottoms for one piececontainers is the possibility of stress cracking in the base. The amountof stress cracking is related to the geometry of the base. Relativelylarge radius curves in the base will reduce the potential for stresscracking compared to a base with small radius curves.

[0009] Yet another factor that is important in the design of suchcontainers is that of positional stability after filling andpressurization of the container. It is preferable, from both a bottler'sand consumer's standpoint, for a filled container to be as resistant totoppling as possible. The stability of a filled container is closelyrelated to the radius of its “outside standing ring,” i.e. the distancethat the bottom contact surfaces of the feet extend from the center axisof the container.

[0010] A further factor that must be taken into account in the design offooted container bottoms is that of efficient distribution of materialwithin the article, so that the article is as “light weighted” aspossible given the necessary strength, volumetric and stabilityrequirements of the container. Light weighting is in particularimportant economically for the manufacturer of the container, since itdirectly impacts material costs.

[0011] A need exists for an improved bottom design for a polymeric onepiece container that will optimize use of material relative to strength,reduce the possibility of stress cracking, permit molding with a minimumof stress and disorientation of the polymer material, and exhibitsuperior resistance against toppling.

SUMMARY OF THE INVENTION

[0012] Accordingly, it is an object of the invention to provide animproved bottom design for a polymeric one piece container that willoptimize use of material relative to strength, reduce the possibility ofstress cracking, permit molding with a minimum of stress anddisorientation of the polymer material, and exhibit superior resistanceagainst toppling.

[0013] In order to achieve the above and other objects of the invention,a molded polymeric container according to one aspect of the invention isshaped to exhibit superior characteristics of light weighting, stabilityagainst toppling and resistance to stress cracking. It includes aconventional cylindrical body portion having a longitudinal axis and acircumferential sidewall and a novel bottom portion. The bottom portionincludes a central pushup area of uniformity that is substantiallyuniform within a spatial rotation about the longitudinal axis. The areaof uniformity has a radius R_(G). The bottom also includes a pluralityof support feet that surround and protrude downwardly from the pushuparea. Each of the support feet have a bottom support surface with aninner point of contact and an outer point of contact. The outer pointsof contact together define an outer contact radius R_(OC). The bottomportion as a whole has a radius of maximum width R_(BASE). A pluralityof ribs are positioned in valleys between the support feet. Each ofthese ribs is positioned between and helps define two of the supportfeet. At least one of the ribs has a localized radius of curvature R_(C)that intersects a line connecting inner points of contact of twoadjacent support feet. Advantageously, the radius of uniformity iswithin the range of about 16% to about 26% of R_(OC); and R_(C) iswithin the range of about 70% to about 110% of R_(BASE).

[0014] According to a second aspect of the invention, a molded polymericcontainer that is shaped to exhibit superior characteristics of lightweighting, stability against toppling and resistance to stress crackingincludes a substantially cylindrical body portion having a longitudinalaxis and a circumferential sidewall; and a bottom portion that includesa central pushup area; a plurality of support feet surrounding andprotruding downwardly from the pushup area, each of the support feethaving a bottom support surface with an inner point of contact and anouter point of contact, the outer points of contacting together definingan outer contact radius R_(OC); and wherein the bottom portion furtherhas a dimension h_(OC) that is defined as the height of the rib directlyabove the circle that is defined by the outer contact radius R_(OC), andwherein$h_{O\quad C} = {\frac{{\Pi \cdot R}\quad b\quad a\quad s\quad {e \cdot {Sin}}\quad \beta}{n \cdot \left( {1 - {{Cos}\quad \beta}} \right)} \cdot \left( {A - \frac{R\quad o\quad c}{R\quad b\quad a\quad s\quad e}} \right)}$

[0015] where n=the number of feet in the bottom; and

[0016] A=a ring index, and wherein A is within a range of about 0.9 toabout 1.15.

[0017] These and various other advantages and features of novelty thatcharacterize the invention are pointed out with particularity in theclaims annexed hereto and forming a part hereof. However, for a betterunderstanding of the invention, its advantages, and the objects obtainedby its use, reference should be made to the drawings which form afurther part hereof, and to the accompanying descriptive matter, inwhich there is illustrated and described a preferred embodiment of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a perspective view of a container that is constructedaccording to a preferred embodiment of the invention;

[0019]FIG. 2 is a side elevational view of the container shown in FIG.1;

[0020]FIG. 3 is a bottom plan view of the container shown in FIGS. 1 and2;

[0021]FIG. 4 is a diagrammatical depiction of certain features of theinvention as it is embodied in the Figures described above; and

[0022]FIG. 5 is a cross-section taken along lines 5-5 in FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0023] Referring now to the drawings, wherein like reference numeralsdesignate corresponding structure throughout the views, and referring inparticular to FIG. 1, a molded polymeric container 10 that is shaped toexhibit superior characteristics of light weighting, stability againsttoppling and resistance to stress cracking includes a conventionalcylindrical body portion 12 having a longitudinal axis 13, shown in FIG.2. As is conventional, container 10 includes a threaded finish portion14, a tapered neck portion 15 connecting the body portion 12 to thefinish portion 14, and a novel and advantageous bottom portion 16.

[0024] In the preferred embodiment, bottom portion 16 includes a centralpushup area 22 of uniformity that is substantially uniform within aspatial rotation about the longitudinal axis 13. The area of uniformityhas a radius R_(G), as is shown in FIG. 4. One of the principles of theinvention is to maximize this relative size of this area 22, which hasthe effect of promoting light weighting of the container 10. Bottomportion 16 also includes a plurality of support feet 18 that surroundand protrude downwardly from the pushup area 22. Each of the supportfeet 18 have a bottom support surface 24 with an inner point of contact26 and an outer point of contact 28. The outer points of contact 28together define an outer contact radius R_(OC), also known as theoutside standing ring of the base. The bottom portion 16 as a whole hasa radius of maximum width R_(BASE). The larger the outside standingring, the greater the stability of the container is against tipping. Inthe preferred embodiment, the outside standing R_(OC) is within therange of about 72% to about 75% of R_(BASE).

[0025] A plurality of ribs 20 are positioned in valleys between thesupport feet 18. Each of these ribs 20 is positioned between and helpsdefine two of the support feet 18. The ribs 20 are preferably of varyingradii of curvature along their length, from near the pushup area 22 towhere they taper into the sidewall 12 of the container. At least one ofthe ribs 20 has a localized radius of curvature R_(C) at a point whereit intersects an arc, with its points equidistant from the axis 13,connecting inner points 26 of contact of two adjacent support feet 18.Advantageously, the radius of uniformity is within the range of about16% to about 26% of R_(OC); and R_(C) is within the range of about 70%to about 110% of R_(BASE). More preferably, the radius of uniformity iswithin the range of about 18% to about 24% of R_(OC); and R_(C) iswithin the range of about 85% to about 100% of R_(BASE). Also within theambit of the invention are ranges of the ratio of the radius ofuniformity R_(G) to R_(OC) having lower values of any value between 16and 20, and upper values of any value between 22 to 26. Further withinthe ambit of the invention are ratios of R_(C) to R_(BASE) within arange that is any combination of a values 70% to 130%.

[0026] As may further be seen in FIG. 4, the localized radius ofcurvature R_(C) defines an angle α_(IC) with respect to the longitudinalaxis 13. The rib 20 has a second localized radius of curvature R_(CG) atthe point where it intersects the outer boundary of the area ofuniformity 22. The radius of curvature R_(CG) defines an angle α_(G)with respect to the axis 13, as may be seen in FIG. 4.

[0027] Advantageously, an angle that is visible in FIG. 4 and is definedas α_(IC) minus α_(G) is within a range of about 16° to about 30°, or,more preferably, within a range of about 18° to about 22°. Ranges withlower end values of between 16° and 18°, and higher end values ofbetween 18° and 22° are also within the ambit of the invention.

[0028] Referring now to FIGS. 4 and 5, it will be seen that the bottomportion 16 further has a dimension h_(OC) that is defined as the heightof the rib directly above the circle that is defined by the outercontact radius R_(OC). This dimension h_(OC) is highly relevant to thecontrol of optimal hoop stretch of the container bottom during formationso that is matches as closely as possible the stretch of the majordiameter section of the container. As may be seen in FIG. 5, which is across-section taken along lines 5-5 in FIG. 4, the side walls of thefeet form angles ∃ with respect to the axis of the instant radius of therib 20 at the point where the vertical projection of the radius R_(OC)intersects the rib 20.

[0029] Optimally, according to one aspect of the invention it has beendetermined that$h_{O\quad C} = {\frac{{\Pi \cdot R}\quad b\quad a\quad s\quad {e \cdot {Sin}}\quad \beta}{n \cdot \left( {1 - {{Cos}\quad \beta}} \right)} \cdot \left( {A - \frac{R\quad o\quad c}{R\quad b\quad a\quad s\quad e}} \right)}$

[0030] where n=the number of feet in the bottom; and A=a ring index, andwherein A is within a range of about 0.9 to about 1.15. More preferably,ring index A is within the range of about 0.95 to about 1.05.

[0031] It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size and arrangement of parts within the principles of the invention tothe full extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

What is claimed is:
 1. A molded polymeric container that is shaped toexhibit superior characteristics of light weighting, stability againsttoppling and resistance to stress cracking, comprising: a substantiallycylindrical body portion having a longitudinal axis and acircumferential sidewall; and a bottom portion comprising: a centralpushup area of uniformity that is substantially uniform within a spatialrotation about the longitudinal axis, said area of uniformity having aradius R_(G); a plurality of support feet surrounding and protrudingdownwardly from the pushup area, each of the support feet having abottom support surface with an inner point of contact and an outer pointof contact, said outer points of contacting together defining an outercontact radius R_(OC); said bottom portion further having a radius ofmaximum width R_(BASE); a plurality of ribs positioned in said valleysbetween said support feet, each of the ribs being positioned between andhelping to define two of the support feet, at least one of said ribshaving a localized radius of curvature R_(C) that intersects an arcconnecting inner points of contact of two adjacent support feet; andwherein said radius of uniformity is within the range of about 16% toabout 26% of R_(OC); and R_(C) is within the range of about 70% to about110% of R_(BASE).
 2. A container according to claim 1, wherein: saidradius of curvature R_(C) defines an angle α_(IC) with respect to saidlongitudinal axis; said at least one rib has a localized radius ofcurvature R_(CG) that intersects an outer boundary of said area ofuniformity, said radius of curvature R_(CG) defining an angle α_(G) withrespect to said longitudinal axis; and and α_(IC) minus α_(G) is withina range of about 16° to about 30°.
 3. A container according to claim 1,wherein said radius of uniformity is within the range of about 18% toabout 24% of R_(OC).
 4. A container according to claim 1, wherein R_(C)is within the range of about 85% to about 100% of R_(BASE).
 5. Acontainer according to claim 2, α_(IC) minus α_(G) is within a range ofabout 18° to about 22°.
 6. A container according to claim 1, whereinR_(OC) is at least about 70% of R_(BASE).
 7. A container according toclaim 6, wherein R_(OC) is within the range of about 72-75% of R_(BASE).8. A container according to claim 1, wherein said rib has a varyingradius throughout its length.
 9. A container according to claim 1,wherein said bottom portion further has a dimension h_(OC) that isdefined as the height of the rib directly above the circle that isdefined by said outer contact radius R_(OC), and wherein$h_{O\quad C} = {\frac{{\Pi \cdot R}\quad b\quad a\quad s\quad {e \cdot {Sin}}\quad \beta}{n \cdot \left( {1 - {{Cos}\quad \beta}} \right)} \cdot \left( {A - \frac{R\quad o\quad c}{R\quad b\quad a\quad s\quad e}} \right)}$

where n=the number of feet in the bottom; and A=a ring index, andwherein A is within a range of about 0.9 to about 1.15.
 10. A containeraccording to claim 9, wherein ring index A is within the range of about0.95 to about 1.05.
 11. A molded polymeric container that is shaped toexhibit superior characteristics of light weighting, stability againsttoppling and resistance to stress cracking, comprising: a substantiallycylindrical body portion having a longitudinal axis and acircumferential sidewall; and a bottom portion comprising: a centralpushup area; a plurality of support feet surrounding and protrudingdownwardly from the pushup area, each of the support feet having abottom support surface with an inner point of contact and an outer pointof contact, said outer points of contacting together defining an outercontact radius R_(OC); and wherein said bottom portion further has adimension h_(OC) that is defined as the height of the rib directly abovethe circle that is defined by said outer contact radius R_(OC), andwherein$h_{O\quad C} = {\frac{{\Pi \cdot R}\quad b\quad a\quad s\quad {e \cdot {Sin}}\quad \beta}{n \cdot \left( {1 - {{Cos}\quad \beta}} \right)} \cdot \left( {A - \frac{R\quad o\quad c}{R\quad b\quad a\quad s\quad e}} \right)}$

where n=the number of feet in the bottom; and A=a ring index, andwherein A is within a range of about 0.9 to about 1.15.
 12. A containeraccording to claim 11, wherein said bottom portion further comprises acentral pushup area of uniformity that is substantially uniform within aspatial rotation about the longitudinal axis, said area of uniformityhaving a radius R_(G) and said radius of uniformity is within the rangeof about 16% to about 26% of R_(OC).
 13. A container according to claim11, wherein said bottom portion further includes a plurality of ribspositioned in said valleys between said support feet, each of the ribsbeing positioned between and helping to define two of the support feet,at least one of said ribs having a localized radius of curvature R_(C)that intersects an arc connecting inner points of contact of twoadjacent support feet; and wherein R_(C) is within the range of about70% to about 110% of R_(BASE).